(1) Field of the Invention
The present invention relates to a control lever for controlling a rotary wing, to a mechanical control system including said lever, and to an aircraft fitted with said control system.
The invention lies in the field of aircraft, in particular rotorcraft, and it relates more particularly to flight control systems that are actuated by a human pilot to control a rotary wing aircraft, more particularly in pitching and in roll. More specifically, the invention relates to control levers for controlling the flight directions of an aircraft, and in particular for modifying the pitch of the blades of the rotary wing fitted to a rotorcraft. In particular, the invention provides a cyclic stick for mechanical transmission of commands, which stick is of a structure that is axially compact.
(2) Description of Related Art
Rotorcraft are commonly fitted with manually-operated control systems to enable a pilot to fly the rotorcraft.
Among such control systems, there is a cyclic control lever that enables the pilot to modify the pitch of the blades in cyclic manner in order to cause the rotorcraft to move in pitching and in roll, and a collective control lever that enables the pilot to modify the pitch of the blades collectively in order to control the rotorcraft in elevation.
The cyclic control lever is hinged to a frame, e.g. arranged in a box or the like, and it is mounted to move in tilting in two control directions that are associated with respective flight controls. The cyclic control lever is hinged to the frame via a distal fixed end, and it is provided at its proximal free end with a handle for gripping. The proximal end is the end of the control lever that can be manipulated by the pilot, while the distal fixed end is the end of the cyclic control lever that is remote from its proximal end.
The collective control lever and the cyclic control lever are generally connected to the blades via mechanical connections referred to as “linkages”, which linkages are secured to a non-rotary swashplate of a set of control swashplates. The rotary swashplate in this set of control swashplates is itself mechanically connected to each blade via a pitch control rod.
More precisely, primary roll and pitching linkages connect a double hinge at a fixed end of a cyclic control lever to a mixing unit, with the mixing unit being connected to the non-rotary swashplate of the set of cyclic swashplates via secondary linkages. Furthermore, the collective control lever is connected to the mixing unit via a collective primary linkage. Under such circumstances, a flight control is connected to the rotary wing via a roll, pitching, or collective linkage that is itself provided in succession with a primary linkage followed by a secondary linkage.
A movement of the cyclic control lever gives rise to a movement of the primary linkage in roll or of the primary linkage in pitching, and consequently it gives rise to a movement of the corresponding secondary linkages via the mixing unit. In contrast, a movement of the collective control lever gives rise to a movement of the collective primary linkage and then to movements of all of the secondary linkages via the mixing unit.
Nevertheless, since the forces that need to be exerted to change the pitch of the blades are large, a servocontrol is generally arranged in each secondary linkage. For example, at least one servocontrol is provided for controlling pitching, referred to as the “pitching servocontrol” for convenience, and two servocontrols are provided for controlling roll, a left servocontrol and a right servocontrol.
When the pilot seeks to modify the collective pitch of the blades, the pilot acts on the collective control lever in order to cause all three servocontrols to raise or lower the set of controlling swashplates.
The pitch control rods are then all moved identically, thereby causing the pitch of all of the blades to vary by the same angle.
In contrast, in order to vary the cyclic pitch of the blades so as to direct the helicopter in a given direction, the pilot causes at least one servocontrol to move by tilting the cyclic control lever appropriately in the desired direction.
The set of controlling swashplates does not move vertically, but rather tilts relative to the mast of the main rotor. Each pitch control rod is thus moved as a function of the intended target so as to generate an appropriate cyclic variation in the pitch of each blade.
Furthermore, when moved cyclically, the set of controlling swashplates needs to tilt about two perpendicular axes. On a light rotorcraft in which the bending stresses on said sets of controlling swashplates are small, the points where the servocontrols are fastened to said sets of controlling swashplates are then located on said axes.
However, on a heavy rotorcraft, it is preferable for the servocontrols to be distributed uniformly, such that they are separated from one another by angles of 120°, assuming that the rotorcraft is fitted with three servocontrols.
The cyclic control lever is then connected via a primary roll linkage and a primary pitching linkage to phasing means that are separate from the cyclic control lever, with the phasing means being connected to the mixing unit via one mechanical connection per servocontrol.
An order for performing a roll or a pitching operation, sometimes referred to as a “pure order” by the person skilled in the art, is then transformed into a composite movement of all of the mechanical connections downstream from the phasing means. Under such circumstances, and strictly speaking, there is then no longer one roll control linkage and one pitching control linkage between the phasing means and the mixing unit. When three servocontrols are used, the three corresponding mechanical connections are sometimes referred to as the “front linkage”, the “left linkage”, and the “right linkage”, depending on the positions of said three servocontrols.
In another aspect, the flight controls of a rotorcraft include pedals also controlling a secondary rotor in yaw by means of a yaw linkage that optionally passes via the mixing unit.
Cyclic control levers include long cyclic sticks or “columns” that are used mainly for transmitting controls manually, and short cyclic sticks that are used mainly for transmitting controls electrically. As an indication, the length of a long cyclic stick is about three to four times the length of a short cyclic stick.
A long cyclic stick has a considerable lever arm that is favorable to transmitting controls mechanically, thereby making it easy for the pilot to manipulate. The pilot then makes use of all of an arm for operating the long cyclic stick with an appropriate amount of force, and can feel directly the opposing forces generated by the remote power members against being operated.
A short stick, of small size, may be arranged on one side of the pilot so as to make the cockpit more ergonomic and release space in front of the pilot. Such a stick is sometimes called a “mini-stick” because of its size that is small compared with the size of a conventional long stick.
Ideally, a considerable compromise is achieved by using an axially short cyclic stick for controlling a rotary wing via a mechanical architecture. Nevertheless, such a mechanical architecture generates high levels of friction, with these friction forces being maximized by the presence of phasing means between the cyclic control lever and the mixing unit. It would then appear difficult to implement a short cyclic stick with mechanical transmission on a rotary wing aircraft, since the lever arm of such a stick would appear to be difficult to make compatible with such friction forces.
The state of the art includes the documents: DE 195 24 282, US 2009/230252, and U.S. Pat. No. 1,550,739.
Document DE 195 24 282 describes a control lever provided with a hinged short stick, said stick extending from a handle to a stand. The stand co-operates with linkages.